This invention relates to electroculture and more particularly to apparatus utilizing electricity for destroying weeds along crop rows.
Weed killing apparatus is known for destroying weeds with electricity such as disclosed in U.S. Pat. No. 3,919,806 wherein a high voltage source of electricity is carried on a vehicle, a coulter wheel grounds the high voltage source, and a conductive elongated horizontal rod mounted on the vehicle and connected to the high voltage source carries a plurality of spaced weed contacting electrodes, such as deflectable conductive spring leaves, adapted to wipe across the plants and transfer electricity thereto. The high voltage source usually comprises an alternating current generator carried on the vehicle and driven by the power take-off drive of the tractor pulling the vehicle and a transformer for stepping up the generator voltage applied to the conductive rod and the weed contacting electrodes.
When a weed contacting electrode wipes across a plant, the high potential of the conductive rod and the electrode causes current to flow through the weed, the earth and the grounding coulter to kill the weed by destroying its cell structure. The high voltage often results in formation of arcs between the electrodes and the plants with flow of relatively high magnitudes of current through the plants to ground. In the open circuit condition when no electrode is in contact with a weed, the high potential V.sub.g at the electrodes is equal to the generator counter EMF voltage CEMF multiplied by the turns ratio (N.sub.1 /N.sub.2) of the step-up transformer, or V.sub.g =CEMF times (N.sub.1 /N.sub.2). When an electrode contacts a weed, the resulting current flow I may be quite high and result in substantial reduction in voltage on the other electrodes due to flow of the current through the impedance of the high voltage source in accordance with the equation V.sub.g =[CEMF-Z.sub.E (I times N.sub.2 /N.sub.1)] times (N.sub.1 /N.sub.2) where Z.sub.E is the equivalent impendance of the high voltage source. Such voltage reduction is even greater when several electrodes connected to the same conductive rod simultaneously contact weeds so that current is flowing in parallel paths through the weeds to ground, and the reduced voltage level Vg on the remaining electrodes may be insufficient to cause significant destruction of weeds contacted by the spring leaves.